1. Field of the Invention
This invention relates to an electronic control apparatus for an internal combustion engine capable of determining failure in a control device for exhaust gas return which controls a return quantity of exhaust gas.
2. Discussion of Background
A conventional electronic control apparatus for an internal combustion engine of this kind is to be explained in FIG. 1.
In FIG. 1, numeral 1 signifies a conventional four cycle spark ignition type engine mounted on an automobile. The engine 1 sucks air for combustion through the air cleaner 2, the suction pipe 3 and the throttle valve 4. Fuel is supplied to the engine 1 by the electromagnetic valve 5 installed at the suction pipe 3 from a fuel system, not shown. At the downstream side of the throttle valve 4 of the suction pipe 3, there is a pressure sensor 6 for detecting an absolute pressure in the suction pipe 3 and converting it to an electric voltage. The throttle sensor 7 detects the opening of the throttle valve 4, and generates an electric voltage corresponding thereto. The electronic engine control device 8 receives the outputs of the pressure sensor 6, a crank angle sensor (not shown), the throttle sensor 7, a cooling water temperature sensor (not shown), and so on, and controls the drive of the electromagnetic injection valve 5, an air control valve 17 and an electromagnetic valve 9.
A part of the exhaust gas separated to the exhaust gas branch pipe 11, which is connected to the exhaust gas pipe 10, returns to the engine 1 by flowing into the downstream side of the throttle valve 4 of the suction pipe 3 via an exhaust gas return, hereafter EGR, control valve 12 which controls the return of the exhaust gas, and the EGR intake pipe 13. The EGR control valve 12 is composed of a well known structure, the constituent parts of which are negative pressure chamber 12A, valve 12B and spring 12C of the negative pressure chamber 12A. The negative pressure chamber 12A is connected to the negative pressure control pipe 14 which is connected in the neighborhood of the downstream side of the throttle valve 4 of the suction pipe 3 via the electromagnetic valve 9. The EGR quantity is controlled by a negative pressure working on the negative pressure chamber 12A through the valve 12B and the EGR intake pipe 13.
Next, the operation of the above device is explained. The electronic engine control device 8 receives the input signals from the pressure sensor 6, a crank angle sensor (not shown), and a cooling water temperature sensor (not shown), and so on, to purify the exhaust gas, especially NO.sub.x, to an optimum condition, and controls the electromagnetic valve 9 by determining the operation or the non-operation of the EGR control valve 12, so that no bad influence is put on the driving condition of the engine 1. First, this electronic engine control device 8 generates a control signal whereby the electromagnetic valve 9 is closed, when the EGR control valve 12 is operated. In this case, the negative pressure chamber 12A and the negative pressure control pipe 14 are connected whereby the valve 12B is in fully open state by the negative pressure at the downstream side of the throttle valve 4. As a result, the EGR is in operation.
The EGR control valve 12 does not operate, when a control signal is outputted whereby the electromagnetic valve 9 is open. In this case the negative pressure chamber 12A is open to the air via pipe 16, which fully closes the valve 12B. Accordingly, exhaust gas is not returned and the EGR is not in operation. The above-mentioned conventional electronic control device for an internal combustion engine has a problem because fault detection of the EGR control system is not possible in the case of failure, malfunction of the EGR control system or clogging of valves and pipes by dirts. As the result, return to the engine of the exhaust gas of a predetermined quantity and deterioration of the exhaust gas, can not be detected.